On Tue, 2008-03-18 at 18:31 -0500, Bob McGraw - K4TAX wrote:
> I suspect that you may have a defective filter. The fact that you had to
> pad an oscillator is a clue. Or maybe a BFO crystal is out of tolerance.
>
> I measured the audio frequency response of my Omni VI Plus using the
> sinewave/power method. Once I did this, I was able to see the shape of the
> filter and take into account the group delay which affects the "sound" of
> the radio. I didn't do a squarewave response however. I also confirmed
> that the DSP artifacts were present in the RX signal regardless of the NR or
> Auto Notch usage.
>
> I've found that the mechanical Collins filters used in the Omni VII offer an
> significantly enhanced signal on SSB both in transmit and receive. They are
> clearly different than crystal filters regardless if they are ladder of
> lattice configuration.
>
> 73
> Bob K4TAX
>
>
Ladder filters inherently have different upper and lower skirt slopes.
They also inherently have a more rounded transition from pass band to
stop band which gives them a much better time response.
The Collins mechanical filter has enough design versatility to allow
symmetry even when neither a ladder or a lattice filter, though the S-
line vintage filters were really bad at ringing. I'm not noticing that
so much with the modern Collins CW filter in my FT-857D.
73, Jerry, K0CQ
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|